1. Technical Field
The present invention relates to analog to digital conversion of optical signals and more a particularly to high speed photonic filter methods and systems.
2. Description of the Related Art
In high-capacity, long-haul fiber data transmission, post detection processing by digital signal processing (DSP) can greatly improve transmission performance by robust compensation against chromatic dispersion (CD) and polarization mode dispersion (PMD), while doubling data capacity by allowing polarization division multiplexing (PDM) through multiple-input multiple-output (MIMO) processing. However, the unavailability of analog-to-digital converters (ADC) at high sampling rates has hindered the real time implementation of post detection DSP at high data rates. For example, 100 Gb/s applications would require sampling rates up to 30-50 GSa/s depending on the modulation format. To bridge the gap between the required sampling speed and what is commercially available, one will need the utilization of multiple ADCs through parallel processing.
Most implementations of high speed ADCs require the use of sample-and-hold circuitry in the electronic domain. In this scheme, an analog input is parallel processed and sampled in a time-interleaved fashion using multiple ADCs, where the timing signal clocking each ADC is precisely skewed. Each one of the sample-and-hold circuits has to cover the bandwidth of the input analog signal, and the timing skew used for each ADC requires extreme precision.